N-Type Triazine Spiro Host for TADF OLED Lifetime

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Solution Overview

Problem

Thermally activated delayed fluorescence (TADF) OLEDs face unsatisfactory stability due to high-energy exciton formation and asymmetric hole and electron mobilities, leading to device degradation and operational reliability issues.

Innovation Solution

Employing n-type hosts with specific triazine ring-substituted spiro aromatic groups to balance charge fluxes, broaden the recombination zone, and suppress high-energy exciton formation, thereby extending the lifetime of TADF OLEDs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional host materials are used in TADF OLEDs, then device efficiency can be maintained, but device stability and operational lifetime are significantly reduced due to high-energy exciton formation and asymmetric charge transport

Engineering Contradiction:

Improvedevice stabilityVSAvoidoperational lifetime

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent changes the fundamental parameter of host material type from conventional p-type or ambipolar hosts to n-type hosts. This parameter change fundamentally alters the charge transport characteristics, enabling balanced electron and hole fluxes, suppressing high-energy exciton formation, and extending device operational lifetime by more than 30 times for green TADF OLEDs and more than 1,000 times for blue TADF OLEDs.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If host materials with high triplet energy are used to confine excitons, then exciton confinement is improved, but charge balance deteriorates due to highly asymmetric hole and electron mobilities in organic semiconductors

Engineering Contradiction:

Improveexciton confinementVSAvoidcharge balance

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent inverts the conventional approach by using n-type hosts instead of p-type or ambipolar hosts. This inversion fundamentally changes the charge transport dynamics, allowing electrons to be the dominant charge carriers that can effectively balance the highly mobile holes, thereby achieving both excellent exciton confinement and balanced charge transport simultaneously.

Inventive Principle:

Principle #13The other way round (Inversion)

3Use of energy by moving object

If direct exciton formation on TADF molecules is achieved, then energy efficiency is improved, but device stability is compromised by the formation of high-energy excitons on host molecules

Engineering Contradiction:

Improveenergy efficiencyVSAvoidhigh-energy exciton formation

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The n-type host acts as an intermediary that facilitates balanced charge transport and suppresses the formation of high-energy excitons on host molecules. By controlling the charge fluxes and recombination zone, the n-type host prevents the harmful formation of high-energy excitons that would otherwise lead to TADF molecule degradation, while still enabling efficient energy transfer to the TADF emitter.

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The use of n-type hosts significantly increases the operational lifetime of green and blue TADF OLEDs by more than 30 and 1,000 times, respectively, achieving stable and efficient device performance.

Implementation Method 1

n-type hosts that have the intrinsic ability to balance the charge fluxes... holes and electrons are injected from opposing electrodes into transport and blocking layers and eventually recombine to form excitons

Methodology Applied

Scientific EffectCharge transport: Conduction (electrical)

Implementation Method 2

electrons and holes directly combine on the TADF emitters to directly form excitons... Direct exciton formation on the TADF molecules can eliminate energy dissipation channels and avoid the formation of high-energy exciton on host molecules

Methodology Applied

Scientific EffectExciton formation: Electroluminescence

Implementation Method 3

This combination allows for efficient Forster and Dexter energy transfer from host to guest and confinement of both singlet and triplet excitons in the guest

Methodology Applied

Scientific EffectFörster energy transfer:

Implementation Method 4

This combination allows for efficient Forster and Dexter energy transfer from host to guest and confinement of both singlet and triplet excitons in the guest

Methodology Applied

Scientific EffectDexter energy transfer:

Implementation Method 5

Non-emissive triplet excitons (T1) are readily up-converted into emissive singlet excitons (S1) in TADF molecules because of their nearly degenerate S1 and T1 states, leading to 100% internal quantum efficiency

Methodology Applied

Scientific EffectThermally activated delayed fluorescence:

Data Source

PatentUS11482679B2Compound, light-emitting lifetime lengthening agent, use of n-type compound, film and light-emitting device

Publication Date: 2022.10.25 KYUSHU UNIV

AI summary

A light-emitting device having a light-emitting layer containing a delayed fluorescence emitter and an n-type compound has an extended lifetime and high performance. A compound having a triazine ring substituted by a spiro aromatic group can be used as the n-type compound.